Photoflash lamp



United States Patent 3,316,968 PHOTOFLASH LAMP Bruce T. Buzalski, Caldwell, N..l., assignor to Westinghouse Electric Corporation, Pittsburgh, Pa, a corporation of Pennsylvania Filed Dec. 27, 1965, Ser. No. 516,652 9 Claims. (Cl. 6731) This invention relates to photoflash lamps and more particularly to a photoflash lamp of the plastic-envelope, chemical-reaction type.

Present commercial photoflash lamps generally employ a sealed glass envelope enclosing a combustible material in shreaded foil form. This foil is usually zirconium, magnesium or aluminum and is disposed in an oxygen atmosphere which may be above atmospheric pressure. An electrically energized filament is generally employed to ignite a primer which causes the foil to react with the oxygen atmosphere to produce the desired flash of light. The problem of rupture of the glass envelope when the lamp is fired is generally overcome by coating the outside surface of the lamp envelope with an organic lacquer. The use of plastic, light-transmitting, photoflash lamp envelopes is highly desirable from the standpoint of both cost of manufacture and safety of operation. The use of plastic photoflash lamp envelopes is, however, not practical in conventional lamps since the plastic will not retain the oxygen atmosphere for an acceptable length of time.

Recent developments in the photoflash lamp field wherein a powdered metal and a solid chemical oxidizing agent have been employed as the flash producing material in plastic photoflash lamp envelopes which have been sealed in and enclose an ambient atmosphere are disclosed in the application of Norman F. Baird, Ser. No. 197,639, filed May 25, 1962, now Patent No. 3,220,224, granted Nov. 30, 1965, and assigned to the same assignee as the present application.

For both glass and plastic photoflash lamps, the press type seal has been used extensively throughout the lamp making industry. After the flash producing material has been disposed within a glass or plastic fiash lamp envelope, the open end thereof is heated and laterally compressed or pinched to seal off the interior of the lamp envelope. With the high temperature, high pressure conditions found in lamps employing the powdered metal and solid chemical oxidizing agent mixture systems, this press type seal has not been wholly satisfactory. The press type seal causes a reduction in envelope wall thickness in the envelope area adjacent the seal and provides a weakened area where either total fracture or tiny holes can occur. When lamps of the chemical reaction type are fired, extremely hot inorganic residue, produced by the chemical reaction are embedded in a random manner, while in a red to white hot condition, in and around the base or sealed end of the plastic tube or envelope. These particles soften the plastic and the substantially simultaneous combustion pressure in the tube can create tiny holes, particularly in the thinner regions of the plastic enclosure. It will be apparent then that when the tube or envelope is sealed in the conventional manner, through lateral compression, the walls of the tube elongate near the edges of the seal thus providing thin wall sections in the area of the seal and thereby enhance the probability of rupture of one kind or another.

The present invention eliminates the problem of wall sections of reduced thickness and in fact provides Walls of increased thickness in the area of the seal by employing a tubular photoflash lamp envelope and a molded cylindrical base member. The tubular envelope carries the flash producing charge While the primer charge carried by the filament mount is disposed in a central cylinice drical well in the base member. To effect a seal, the tubular walls of the photoflash lamp envelope are inserted to a substantial depth in a deep annular slot or groove in the base member and sealed therein.

It is accordingly an object of the present invention to provide a plastic photoflash lamp which will neither frac ture nor rupture under high pressure, high temperature conditions.

Another object of this invention is to provide a plastic photoflash lamp having accurately predictable dimensions.

A further object of the present invention is to provide a plastic photoflash lamp which is economical and simple to assemble.

Yet another object of this invention is to provide a photoflash lamp having consistently reproducible dimensional characteristics.

These and other objects and many of the attendant advantages of this invention will become readily apparent as the same becomes better understood by reference to the following detailed description when considered in connection with the accompanying drawings, in which:

FIGURE 1 is a sectional view of the photoflash lamp of the present invention; and

FIG. 2 is an exploded view of the photoflash lamp tube and base member of the photoflash lamp of the present invention.

Referring now in detail to the drawings, there is shown in FIG. 2 a radiation-transmitting, high-strength, molded plastic tube 10 and a cylindrical plastic base member 12 which comprise the principal parts of the photoflash lamp of the present invention. As can be seen in FIG. 1, the walls of tube 10 at its open end are received in a deep annular slot or groove 14 in base member 12. Centrally of annular slot 14 is a frustoconical chamber 16 which converges from the top end of base member 12 into a cylindrical ignitor well 18.

A conventional filament mount for this type photoflash lamp is positioned within ignitor Well 18. The filament mount includes a pair of lead-in conductors 22, a glass head 24 and a primer charge 26 carried by a filament which connects lead-in conductors 22.

Located, for example, by being afiixed to the upper end of photoflash lamp tube 10 is the flash producing material 28. This flash producing charge or material is generally a mixture of 'a predetermined amount of finely divided solid oxygen liberating substance and a predetermined amount of finely divided metallic substance. Examples of these materials may be found in the above referred to application Serial No. 197,639, and may include zirconium as the metal and barium nitrate, strontium nitrate or potassium chlorate as the oxygen liberating substance.

Any"radiation-transmitting, high-strength thermoplastic may be employed for envelope 10 and base 12, however, extruded or injection molded cellulose propionate is particularly suited for this purpose. The lower extremities of the walls of tube 10 may be sealed within the annular slot 14 of base 12 in any one of several ways which will be apparent to those skilled in the art. For example, since tube 10 and base member 12 are preferably of the same thermoplastic material, any suitable solvent for the plastic such as acetone may be employed to effect the seal. Epoxy cement as well as several commercially available glues which have good adhesion when used with plastic are also suitable for sealing the tube 10 within annular slot 14. Alternatively, a heat seal could also be effected between the two parts with the heat being applied laterally of base 12. In the case of cellulose propionate, heating laterally from about to C. will permit fusion of the tube 10 and the base member 12 without undue deformation of ignitor well 18.

Ignitor well 18 provides both a heat sink for the leadin conductors, which become quite hot during the reaction, and further serves to isolate the ignitor from the relatively thin walls of tube 10. The conical surfaces of chamber 16 serve to direct hot particles from the ignitor or primer charge toward the top of the tube Where they react with the flash producing charge 28. The sloping surfaces of chamber 16 further serve to direct the molten metal away from the side Walls of tube 10 and prevent a collection of the hot material on the thin bulb or tube wall which could, on occasion, cause the wall of the tube to melt at the point of contact thus resulting in hot particles and gas being ejected from the bulb or tube due to the high pressure.

It will be apparent from the foregoing that the present invention provides an improved plastic photofiash lamp of the solid chemical mixture type which has predictable dimensional consistency, will not fracture or rupture upon firing, and is characterized by simplicity and ease of assembly.

Since numerous changes may be made in the above described photofiash lamp and diiferent embodiments of the invention may be made without departing from the spirit or scope of the present invention, it is intended that all matter contained in the foregoing description or shown in the accompanying drawings shall be interpreted as illustrative and not in a limiting sense.

I claim as my invention:

1. A photoflash lamp comprising:

(a) a radiation transmitting sealed plastic envelope having a flash producing material disposed therewithin;

(b) a preformed plastic base having a central cavity portion and a filament mount including a primer charge mounted in the central cavity of said base;

() said base including a deep annular slot adapted to receive one end of said plastic envelope; and

(d) means for sealing said one end of said plastic envelope Within said deep annular slot.

2. A photoflash lamp according to claim 1 wherein said plastic envelope and said plastic "base are of the same material.

3. A photofiash lamp according to claim 1 wherein said means for sealing is an epoxy cement.

4. A photofiash lamp according to claim 1 wherein the outer surface of said one end of said envelope is sealed to the outer wall of said annular slot and the inner surface of said one end of said envelope is sealed to the inner wall of said annular slot.

5. A photoflash lamp of the chemical-mixture flashproducing type comprising:

(a) a tubular, optically-light-transmissive,

strength, molded plastic envelope;

(b) a flash producing material mounted therewithin;

(c) a molded plastic base member having a tapering central cavity and a deep annular groove surrounding said central cavity;

(d) a filament mount including a pair of lead-in conductors and an ignitor carrying filament mounted within said cavity; and

(e) an extensive seal between a substantial portion of the walls of said tube and the walls of said annular groove.

6. A photofiash lamp according to claim 5 wherein said tapering central cavity comprises a frustoconical bore converging from the upper end of said base portion into a filament mount receiving cylindrical bore extending proximate the bottom end of said base portion.

7. A photoilash lamp according to claim 5 wherein said seal is formed of epoxy cement.

8. A photoflash lamp according to claim 5 wherein said seal is aheat seal. 7

9. A photofiash lamp according to claim 5 wherein said seal is produced by a solvent for said base and said envelope.

high- References Cited by the Examiner UNITED STATES PATENTS 2,277,481 3/1942 De Margitta 67-31 JAMES W. WESTHAVER, Primary Examiner 

1. A PHOTOFLASH LAMP COMPRISING: (A) A RADIATION TRANSMITTING SEALED PLASTIC ENVELOPE HAVING A FLASH PRODUCING MATERIAL DISPOSED THEREWITHIN; (B) A PERFORMED PLASTIC BASE HAVING A CENTRAL CAVITY PORTION AND A FILAMENT MOUNT INCLUDING A PRIMER CHARGE MOUNTED IN THE CENTRAL CAVITY OF SAID BASE; (C) SAID BASE INCLUDING A DEEP ANNULAR SLOT ADAPTED TO RECEIVE ONE END OF SAID PLASTIC ENVELOPE; AND (D) MEANS FOR SEALING SAID ONE END OF SAID PLASTIC ENVELOPE WITHIN SAID DEEP ANNULAR SLOT. 